We released three versions with it being disabled and it doesn't look
like it will come back any time soon. Also the build was broken at least
since the repo splitting due to incorrect path to dbus xml.

In addition the connection to decorations got dropped already with the
change to kdecoration2. Which means it anyway needs large adjustements
to get the code working again.

Overall it doesn't look like it makes lots of sense to keep the code
around for someone working on it in future. If that happens this change
can be reverted.